This invention relates to plant growth hormone compositions. More particularly, the present invention relates to gibberellin compositions and a method of increasing the efficacy of gibberellins.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date:
(i) part of common general knowledge; or
(ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.
The agricultural industry has found that the use of plant growth hormones can aid in the control of crop quality and thus the value of the harvest. Plant growth hormones evidence several effects including the ability to either stimulate or inhibit growth. There are five major groups of plant hormones: auxins, gibberellins, ethylene, cytokinins and abscisic acid. The more commonly used groups in agriculture at the moment are the auxins, gibberellins, ethylene and cytokinins.
The gibberellins, which include gibberellic acid or GA-3, are responsible for promoting growth in most plants. They are, for example, known to cause growth in dwarf mutants so that they are indistinguishable from normal tall, non-mutant plants. Seed germination can be hastened by application of gibberellins. Some plants have different juvenile and adult growth and gibberellins applied to a bud on adult growth will cause formation of juvenile growth. Application to plants which form rosettes before flowering will induce bolting and flowering. Gibberellins also stimulate pollen germination. Parthenocarpic fruit can be caused by gibberellins in some fruits such as apples, currants, cucumbers, eggplants, mandarin oranges, almonds and peaches.
Gibberellins are used commercially to increase fruit size and their set and cluster sizes. For example, application of gibberellins to grapes is well known. It also induces a much looser appearance to the cluster of grapes. Other areas of known uses of gibberellins include delaying the ripening of citrus fruit on trees, stimulating flowering of strawberries and stimulating the partial digestion of starches in germinating barley during the process of brewing beer.
The gibberellins cannot be easily directly applied to a crop and require a solvent system as a carrier for such applications. Further, gibberellins are slowly hydrolysed in aqueous solutions and therefore cannot be stored long term in aqueous solutions. Commercial solutions are thus non-aqueous. Gibberellins are currently dissolved in alcohol solutions, particularly methanol. Methanol is both flammable and poisonous. The Dangerous Goods Authorities therefore demand that all products which contain methanol, including gibberellin solutions, be marked as both flammable and poisonous and handled accordingly.
For application, the farmer dilutes the methanol gibberellin (usually gibberellic acid) solution with water and then this is sprayed onto the crop. Numerous applications of this gibberellin spray are necessary to achieve the desired effects. When used on grape vines, the first applications, typically two, are termed thinning sprays because their timing is designed to reduce the number of grapes per bunch. The later applications are used to increase the size of the grapes and are called sizing sprays. It is recognised that whilst the gibberellin is xe2x80x98taken-upxe2x80x99 through the foliage of the plant, the cuticle of the foliage is covered with a thin layer of wax which renders it hydrophobic and difficult to permeate. As a result, the uptake by the foliage of gibberellin in an aqueous solution is not efficient. This inefficiency is further increased when the methanol and water have evaporated leaving the gibberellin as a xe2x80x98depositxe2x80x99 on the foliage. As gibberellins are expensive, the farmer is always balancing the cost of such applications against the increase in the price of the fruit that may be achieved.
In relation to fruits (eg. grapes, citrus fruits and strawberries), their perceived quality and thus sale value is measured in part by the size and colour of the fruit. A cost-effective method which would
increase the size of fruit;
achieve fruit maturity at an earlier date; and
eliminate any undesirable flammable/poisonous carrier would therefore be of value to the grape grower.
Accordingly, investigations have been carried out in an effort to achieve one or more of these goals.
It has been found that the lack of solubility of gibberellins in lipophilic solvents has been overcome through the use of certain lipophilic solvent systems. This is of interest because they are not flammable like the lower alcohols such as methanol.
According to the invention, a plant growth promoter composition is provided comprising:
(a) not in excess of 20% by weight of one or more gibberellins; and
(b) an essentially non-aqueous solvent system comprising:
(i) 30 to 99% by weight of one or more lipophilic solvents;
(ii) at least an equivalent molar amount to the gibberellin(s) of one or more lipophilic alkaline coupling agents which enable the gibberellin(s) to form a lipophilic solvent soluble complex;
(iii) 1 to 50% by weight of one or more emulsifiers which blend with the lipophilic solvent(s) to form a homogeneous product and enable dispersion of the composition into water for application; and
(iv) optionally, not in excess of 15% by weight of one or more viscosity reducing co-solvents.
It was further found that when gibberellins are used with this solvent system, the growth promoting activity of gibberellins in fruit, and in particular grapes, is enhanced. In particular, use of the solvent system produces grape berries of earlier maturity, larger dimensions and a better appearance showing less russetting (pitting) and less discoloration.
According to a second aspect of the invention there is provided a method for enhancing the efficacy of at least one gibberellin acting as a plant growth promoter comprising the step of incorporating gibberellins into plant growth promoter compositions comprising:
(a) an essentially non-aqueous solvent system comprising:
(i) 30 to 99% by weight of the total composition of one or more lipophilic solvents;
(ii) at least an equivalent molar amount to the gibberellin(s) of one or more lipophilic alkaline coupling agents which enable the gibberellin(s) to form a lipophilic solvent soluble complex;
(iii) 1 to 50% by weight of the total composition of one or more emulsifiers which blend with the lipophilic solvent(s) to form a homogeneous product and enable dispersion of the composition into water for application; and
(iv) optionally, not in excess of 15% by weight of the total composition of one or more viscosity reducing co-solvents.
The gibberellins may be any member of the gibberellin family known to those skilled in the art. Preferably, the gibberellin is gibberellic acid (Gibberellin A-3). Preferably, the amount of gibberellins is in the range of 1 to 15% by weight. More preferably, the amount of gibberellins is in the range of 4 to 10% by weight. The current commercial products contain either 4 or 10% by weight gibberellins.
The lipophilic solvents which can be used include mineral oils, waxes and other petroleum fractions; vegetable and animal oils, fats and waxes and their simple esters; and fatty alcohols and/or synthetic branched chain alcohols and their esters. Preferably, the amount of lipophilic solvent is in the range of 40 to 80% by weight of the total composition.
Preferably, the lipophilic solvents are esters of vegetable oils, in particular, one or more alkyl esters of fatty acids, such as ethyl oleate. There are innumerable variations of the esters of vegetable oils since the alkyl esters of fatty acids may be produced from the combination of any one or more of the lower alcohols whilst the fatty acid moiety can be derived from the natural oils and fats such as lard, tallow and vegetable oils or from specific blends produced by fatty acid manufacturers or from fatty acids produced by synthetic means or their blends. Readily available commercial vegetable oils such as canola, corn, sunflower and soyabean oils are also sources for fatty acids.
Typically, the lipophilic alkaline coupling agents are selected from the following lipophilic solvent soluble bases:
(a) quaternary ammonium hydroxides, overbased phenates, overbased sulphonates;
(b) aromatic, arylalkyl, alkylaryl and polycyclic amines; and
(c) fatty amines and fatty imidazolines.
A suitable commercially available lipophilic alkaline coupling agent is dimethyl cocoamine. Preferably, the lipophilic alkaline coupling agent is a mixture of dimethyl cocoamine and oleylamine. Preferably, the amount of lipophilic alkaline coupling agent used is a molar excess to the amount of gibberellins used. Typically, the amount of lipophilic alkaline coupling agent is in 30% molar excess to the amount of gibberellins.
The properties of the emulsifier system which comprises one or more emulsifiers, will be well known to those skilled in the art and it is recognised that there are a multitude of suitable combinations. Those skilled in the art will note that emulsifiers of certain types may disturb the lipophilic solvent soluble complex, eg acids or anionics, and that these emulsifiers should be avoided. The emulsifier system will be easily blended with the lipophilic solvents to furnish a homogeneous product and to enable dispersion, into water for application. Families of emulsifiers known to provide suitable emulsification of such lipophilic solvents include sorbitan esters and ethoxylates, alcohol ethoxylates, fatty acid ethoxylates (PEG esters), difatty alkyl imidazoline derivatives and fatty betaines. It is recognised that other surfactant types either alone or in combinations may also provide suitable emulsification. Preferably, the amount of emulsifiers used is in the range from 3 to 20% by weight of the total composition.
Viscosity reducing co-solvents will be known to those skilled in the art and include simple alcohols and monoalkyl ethers. If a high flash point is to be maintained, the viscosity reducing co-solvent should be a glycol, diglycol or diglycol ether.